Objective To investigate the effects of special siRNA targeting TLR4 gene (TLR4-siRNA) on hyperoxia-induced secretion of inflammatory factors from human alveolar epithelial cell line A549.Methods Human alveolar epithelial cell line A549 was purchased from Chongqing Children Hospital and cultured in six-well tissue culture plates and randomly divided into 4 gorups:A549 cells + ambient air group (group C) ; A549 cell + hyperoxia group (group H); A549 cells transfected with TLR4-siRNA + hyperoxia group (group TR) and A549 cells transfected with control-siRNA + hyperoxia group (group NR).TLR4-siRNA and control-siRNA were transfected into A549 cells through lipofectamine 2000.The efficiency of transfection was assessed by detection of FAM expression using flow cytometry.The cells were exposed to 95% O2-5% CO2 delivered at 1 L/min for 30 min in groups H,TR and NR.TLR4 mRNA and protein expression was detected by RT-PCR and cytometry respectively.The NF-κB activity in A549 cells was measured by EMSA and the IL-6 and IL-8 levels in supernatant were determined by ELISA.Restults Hyperoxia significantly up-regulated TLR4 mRNA and protein expression and increased NF-κB activity in cells and IL-8 and IL-6 concentrations in supematant in group H as compared with group C.Transfection with TLR4-siRNA significantly attenuated hyperoxia-induced up-regulation of TLR4 mRNA and protein expression and increase in NF-κB activity in the cells and IL-6 and IL-8 concentrations in supernatant in group TR as compared with group H,but transfection with control-siRNA did not.Conclusion TLR4-siRNA could significanly inhibit hyperoxia-induced secretion of inflammatory factors from human alveolar epithelial cell line A549. Key words: Toll-Like receptor4; RNA, small interfering; Hyperoxia; NF-kappa B; Interleukins